There has been a long hiatus from posting here on H2VP. Justin and I are back with a vengeance, however, and we have just returned from the annual meeting for the Society of Vertebrate Paleontology. SVP 2011 was held in Las Vegas, Nevada, and was an exceptionally good time. We attended some excellent talks (puls some weaker ones) and will be blogging about SVP extensively over the next week.
In the meantime, however, I am a co-author on a new paper in PLoS ONE. The citation is:
Dyke GJ, Wang X, Habib MB, 2011 Fossil Plotopterid Seabirds from the Eo-Oligocene of the Olympic Peninsula (Washington State, USA): Descriptions and Functional Morphology. PLoS ONE 6(10): e25672. doi:10.1371/journal.pone.0025672
The paper concerns relatively early members of an extinct seabird group call plotopterids. Some of these grew quite large (up to 6 feet in length, potentially), and all of the known taxa appear to have been flightless, wing-propelled divers.
As some of you may know, I have a bit of a thing for wing-propelled swimming birds, and I published a biomechanical analysis of them in 2010 entitled "The structural mechanics and evolution of aquaflying birds". One of the primary points in the paper is that the biomechanics and swimming dynamics of penguins are quite different from other living wing-propelled birds. In particular, penguins have a mirrored stroke, meaning that the upstroke and downstroke produce similar propulsive forces. In contrast, the other living aquaflying birds use mostly the downstroke to propel themselves through the water (though the upstroke does add some thrust). The mirrored stroke system appears to be reflected in the particularly broad forelimb bones of penguins (photo above copyright by L. Henricks, 2009).
This raises the following question: are penguins unique in this way because they are flightless?
If so, then other flightless aquaflyers should have similar bone mechanics. As such, we compared plotopterids to both living alcids and penguins. We found that plotopterids, while they had similar hindlimb mechanics to living penguins (suggesting lots of walking), did not actually have similar forelimb shape to penguins. Instead, plotopterid forelimbs are more comparable to alcids, which we take to suggest that plotopterids did not use the penguin-style swimming stroke.
If we are correct, then penguins are unique for reasons beyond simply being flightless wing-propelled swimmers. The full story on the acquisition of the unique penguin swimming mode will likely be revealed by careful biomechanical study of their fossil history...